1. Technical Field
The present invention relates to a secondary battery, and more particularly, to a battery module that is constructed by connecting a plurality of unit batteries to each other.
2. Related Art
Unlike a primary battery that cannot be charged, a secondary battery is rechargeable. Secondary batteries have been manufactured in various shapes, for example, a cylindrical shape, a square shape, or the like.
A secondary battery having a small capacity is used as a power source for various portable small-sized electronic apparatuses such as cellular phones, notebook computers, and camcorders. A secondary battery having a large capacity is commonly used as a motor driving power source for hybrid vehicles or the like.
A plurality of secondary batteries each having a high output are commonly connected in series to each other to constitute a secondary battery having a large capacity capable of being used in driving motors, such as apparatuses requiring a large power, for example, an electric vehicle or the like.
As such, one secondary battery having a large capacity (hereinafter, simply referred to as a battery module throughout the specification) is composed of a plurality of secondary batteries (hereinafter, simply referred to as unit batteries throughout the specification) connected in series to each other
Each unit battery includes an electrode assembly in which an anode plate and a cathode plate are laminated with a separator interposed therebetween, a case having a space in which the electrode assembly is disposed, a cap assembly which is coupled with the case so as to shield the case, and anode and cathode terminals which are electrically connected to collectors of the anode and cathode plates which protrude toward the cap assembly and are provided in the electrode assembly.
The plurality of unit batteries are disposed in a line, conductors are connected between the cathode and anode terminals of adjacent unit batteries through nuts, and the battery module is formed.
In the above-mentioned battery module, several to several tens of unit batteries are connected to each other to constitute one battery module. Therefore, an end-plate is used to fix the laminated unit batteries.
The end-plates are located at the outermost sides of the laminated unit batteries, are fastened by the connection rods and the nuts, and are tightened up. The unit batteries are fixed between the end-plates. According to this structure, the end-plate is applied with strong stress by the nut.
If the end-plate is formed using a high strength material in order to ensure the strength of the end-plate, a manufacturing cost of the end-plate and the battery module increases. For this reason, the thickness of the end-plate is typically increased to increase the strength of the end-plate, so that deformation or destruction of the end-plate is prevented.
However, if the thickness of the end-plate is increased, the total weight of the battery module is increased, so that the performance of an apparatus on which the battery module is mounted is lowered.
It may be beneficial to decrease the weight of secondary batteries for driving motors used in apparatuses such as a hybrid electric vehicle (HEV), a motor bicycle, a motor scooter or the like in order to improve the performance of the apparatuses. However, according to the related art, there is a problem in that the weight of the battery module is increased and the output of the battery module is decreased, so that these battery modules are typically not used for driving such motors.